1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device having a touch panel.
2. Description of the Related Art
Recently, as various portable electronic devices such as mobile phones, PDAs, notebook computers, and the like, and large electronic devices have been developed, the demand for lighter, thinner, shorter, and smaller flat panel display devices has been on the rise. Liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), vacuum fluorescent displays (VFDs) have been actively researched as flat panel display devices.
Meanwhile, personal computers, portable communication devices, and other personal-dedicated information processing devices generally configure interfacing with users by using various input devices such as a key board, a mouse, a digitizer, and the like. However, as portable electronic devices have been advanced, user-inputting cannot be performed on some portable electronic devices by using the input devices such as a key board, a mouse, or the like, and a touch panel allowing the user to directly touch a screen with his hand, a stylus pen, or the like, to input information has been proposed.
According to a method of sensing a contact portion (or a touched portion), a touch panel is classified into a resistive type touch panel, a capacitive type touch panel and an electromagnetic type touch panel. The resistive type touch panel senses a touched position on the screen based on a change in a current according to a resistance in a state in which a DC voltage is applied to a metal electrode formed on an upper plate or a lower plate. The capacitive type touch panel senses a position of an upper or lower plate in which a voltage is changed according to a contact or a touch applied thereto by forming an equipotential on a conductive film. The electromagnetic type touch panel senses a touched position on the screen by reading an LC value induced as an electronic pen comes in contact with a conductive film, and the like.
Touch panels are convenient to use and easy to carry around since they allow text inputs without the necessity of an input device. Such touch panels have recently been applied to various information processing devices and are becoming popular among various users.
FIG. 1 is a cross-sectional view of a related art touch panel-mounted liquid crystal display (LCD) device.
As illustrated in FIG. 1, the related art touch panel-mounted LCD device includes a liquid crystal panel 10 for displaying an image, a touch panel 20 for sensing touches to the panel 20 when a user touches a certain region and transferring position information corresponding to the touched portions, and a bonding layer 30 for bonding the liquid crystal panel 10 and the touch panel 20. The bonding layer 30 is disposed between the liquid crystal panel 10 and the touch panel 20. First and second polarizers 14a and 14b can be provided on the bottom and top surfaces of the liquid crystal panel 10, respectively. Here, a tempered substrate (or an enhanced, reinforced, strengthened substrate) 50 is disposed on an upper portion of the touch panel 20 to prevent damage to the touch panel 20 due to any collision with the exterior and other external factors.
The liquid crystal panel 10 is composed of: a first substrate structure 11 including data lines, gate lines, thin film transistors (TFTs) and various electrodes such as pixel electrode, or the like, formed therein; a second substrate structure including a color filter layer formed therein; and a liquid crystal layer 13 formed between the first substrate 11 and the second substrate 12. The first and second substrate structures 11 and 12 are also referred to as a TFT array substrate and a color filter substrate, respectively.
The touch panel 20 includes a transparent support substrate 21, a plurality of first electrodes 22 formed to be spaced from one another by a certain interval under a lower surface of the transparent support substrate 21, a first insulating layer 23 formed below the entire lower surface of the transparent support substrate 21 including the plurality of first electrodes 22, a plurality of second electrodes 24 formed to be spaced apart from one another by a certain interval and extending in a direction perpendicular to the plurality of first electrodes 22 below the first insulating layer 23, and a second insulating layer 25 formed below the entire surface of the first insulating layer 23 including the plurality of second electrodes 24.
Here, the plurality of first electrodes 22 and the plurality of second electrodes 24 are formed to cross each other with the first insulating layer 23 interposed therebetween, and capacitance is formed in the crossings of the first electrodes 22 and the second electrodes 24. The touch panel 20 senses a position in which the capacitance is changed due to a contact with the outside, thereby sensing the contact portion.
The liquid crystal panel 10 and the touch panel 20 having the forgoing structures are bonded by the bonding layer 30. That is, the liquid crystal panel 10 and the touch panel 20 are spaced apart from each other with the bonding layer 30 formed therebetween for bonding the liquid crystal panel 10 having the second polarizer 14b thereon and the touch panel 20 to the bonding layer 30. The tempered substrate 50 is attached to an upper surface of the transparent support substrate 21 of the touch panel 20. As such, a touch panel-mounted LCD device is fabricated.
However, the touch panel-mounted LCD device having the foregoing structures has at least the following problems and limitations.
In the foregoing touch panel-mounted LCD device, the entire touch panel is attached to the outside of the liquid crystal panel and separate from the liquid crystal panel. Thus, when the LCD device is completed, the overall size of the LCD device is increased by the touch panel attached to the outside of the liquid crystal panel. Also, since the touch panel and the liquid crystal panel are fabricated through separate processes, fabrication costs are increased.
In an effort to address these problems, a structure in which the entire touch panel is formed all within or inside a liquid crystal panel has been proposed. In this case, however, signal interference occurs due to a touch wiring, transmittance is degraded due to the touch wiring which degrades the image quality of the LCD device, and the thickness of the liquid crystal panel is increased, which limits the size reduction of the LCD device. In addition, a process of fabricating the liquid crystal panel is complicated.